of Greenland is, in a great measure, attributable to the agency exerted by these
cavities in breaking up the masses after the process of thawing or, in other words,
ice-decay has proceeded to a certain extent. The growth of ice, as is well
known, takes place from above downwards : that is to say, the uppermost layer
of a frozen surface is the one which was first generated ; the same rule holds
good with each subsequently formed layer in relation to those below it again ;
so that the undermost layer is necessarily the one last produced.
Under the influence of winds and waves, a certain quantity of the atmospheric
air with which sea-water is invariably charged is constantly being given off again
at the surface. The moment a pellicle of ice forms, it precludes the escape of the
air-bubbles, and they become frozen into the ice-mass at a time when, from the
reduction in temperature, they are very much reduced in volume.
In the case of icebergs the same result takes place, although in a somewhat
different manner. Berg-ice, as is well known, is produced on land, and is, in
reality, snow solidified under enormous pressure. Here, then, the case is
reversed, the undermost layer being the oldest of the series. Consequently the
air entangled in the snow-flakes, also at a time when reduced in volume by cold,
becomes more and more compressed, whilst the substance -within which it is
imprisoned becomes more and more solidified. Now the very cause that brings
about the decay of ice, namely, elevation of temperature, produces the expansion
of the air contained in the chambers ; and thus the expansive force operates
precisely at the moment when it has the’ slightest amount of resistance to overcome.
Hence the little detonations, and the disruption of the ice-masses that
attends them.
The tubular cavities proceed from the dismption of the air-cells on the
under surface of ice-masses, whenever the temperature of the water rises sufficiently
to produce thaw. The air-bubble, unable to escape, continues to press
upwards, whilst the access of the water to the interior of the chamber gradual!)’
eats away the walls. A vertical tube is the result, the upper portion of which is
occupied by the now somewhat expanded air-bubble, whilst the lower portion is
filled with water. This boring goes on untü the water within the tube reaches
the level of the surrounding surface, but there it necessarily stops ; and we can
accordingly account for the uniform honeycomb character so constantly presented
on one surface of ice-masses. When, by collision or force of any kind, ice is
broken up in a line parallel to its line of floatation, these tubes sometimes penetrate
through and through; and in this state I found nearly the whole of the
smaller pieces today.
The occurrence of a great number of these cavities at the base of small pieces
of ice must also tend materially to influence their submergence, and cause them
to tilt over, should the boring action proceed more rapidly in one direction than
another.
I have been induced to dwell on this subject, inasmuch as the extremely rapid
disappearance of the ice that besets the coast of Greenland for certain months of
the year has been regarded either as wholly inexplicable, or has been attributed
to a cause which involves an impossibility, namely, its sinking to the bottom
en masse. From what took place during the last few days of our stay at Goodhaab,
coupled with the remarkable condition of the ice just described, there can
hardly be a doubt that during a very brief continuance of sunshine the entire
dissolution of masses of ice many feet in thickness may occur in this manner.
Of course the same kind of decay -would destroy a hundred square miles of ice
as readily as a hundred square inches.
Towards evening land was in sight, but the weather was too thick to see it
plainly. Much snow was, however, visible on the higher ranges; and here and
there along the coast, the pack could be discerned hemming it in. Our prospect
of reaching Julianshaab tomorrow is, therefore, a poor one.
Aug. 17.—Owing, I suppose, to the powerful north-westerly current, we are
still well to the northward of Cape Desolation. Last night the ‘ Bulldog,’ under
sail only, and with a light breeze blowing, came in for some heavy bumps, one large
mass of ice seeming intent on trying conclusions with the starboard paddle. The
damage done was only trifling, however. We are now running down in the
direction of Cape Farewell under steam and sail, with the "wind right aft. The
ice forms a belt commencing about three or four miles from us, and stretches
away to the land, which is distant about forty or forty-five miles. Whilst I
write, the ship is receiving some heavy concussions.
Aug. 18.—This afternoon Cape Christian was sighted to the north-eastward,
—the ice extending along the coast in a vast unbroken field of forty miles in
diameter, and apparently increasing in quantity as the stream passes round
Cape Farewell. The ‘ Bulldog ’ is now quite clear of the pack, and has made